The reaction rate constants of enzyme catalyzed reactions are being determined under steady-state conditions by non-invasive 2D NMR spectroscopic techniques. The 2D NMR technique permits the simultaneous determination of all of the rate constants involved in a reaction sequence, and explicitlly displays them in the form of a 2D plot. In addition, the 2D NMR experiment also provides information on the relative size of the substrate pools involved in the reaction, critical information for determining reaction rates in the compartmentalized cell cytosol. To date, three enzyme systems have been studied; phosphoglucose isomerase, adenylate kinase, and creatine kinase. In all three cases, unique information on both the mechanism and flux charateristics of the reactions have been obtained. Due to the non-invasive nature of the technique, it should be readily applicable to the determination of enzyme reaction rates within intact cells in vitro as well as in vivo.